where str is a nonempty string that represents the desired
directory (see pathname). This command sets the connected book
directory (see cbd) to the string representing the indicated
directory. Thus, this command may determine which files are
processed by include-book and certify-bookcommands typed at the
top-level. However, the cbd is also temporarily set by those two
book processing commands.

IMPORTANT: Pathnames in ACL2 are in the Unix (trademark of AT&T)
style. That is, the character ``/'' separates directory components
of a pathname, and pathnames are absolute when they start with this
character, and relative otherwise. See pathname.